The long-term objective of the research is to significantly extend the range of drugs for which the oral mucosa is a viable route of administration. Specifically, the potential of the oral mucosa as a systemic portal for new therapeutic agents such as peptide drugs, which are currently being developed will be examined. Our goals are (1) to determine the physicochemical environment of the pathways of permeation; (2) to determine the changes that take place in this environment over time, as the result of enhancement, and as a function of the permeant; and (3) to derive predictive algorithms that can be used to estimate the rate and extent of a compound's absorption through the oral mucosa. The specific aims are (a) to identify and characterize the pathways of penetration in real time within intact, freshly-excised (unfixed) samples of oral mucosa, using laser scanning confocal microscopy (LSCM) to optically section the tissue, and further, to localize rate-limiting regions for substances of interest (e.g., fluorescently-labeled peptides and proteins); (b) to visualize, with LSCM, the effects of permeability enhancement on these pathways (e.g.,the promotion of a transcellular pathway) and on the epithelium itself (e.g., changes in cell shape or volume) in the intact, unfixed tissue; and (c) to investigate the relationships between flux and penetrant physicochemical properties (charge, size, lipophilicity) so as to develop predictive models for mucosal permeation. The principal experimental strategies are (i) the use of laser-scanning confocal microscopy (LSCM) and fluorescent probes to image the routes and rates of permeant flow across the oral mucosa, physicochemically characterize these routes, and examine the physiological state of the tissue; and (ii) the development of a unique microcomputer-based physicochemical database which codifies flux parameters extracted from the literature on mucosal permeability, ongoing research in this IRPG, and physical chemistry data from standard references, and the derivation of predictive ('structure-activity') algorithms to calculate mucosal permeability. Overall, a detailed mechanistic examination of permeability of oral tissue is outlined. The research proposed is a part of an Interactive Research Project Grant coordinated by C.A. Squier, University of Iowa.